METHOD FOR PURIFICATION OF 225AC FROM IRRADIATED 226RA-TARGETS

Abstract

The present invention describes a method for purification of .sup.225Ac from irradiated .sup.226Ra-targets provided on a support, comprising a leaching treatment of the .sup.226Ra-targets for leaching essentially the entirety of .sup.225Ac and .sup.226Ra with nitric or hydrochloric acid, followed by a first extraction chromatography separating .sup.25Ac from .sup.226Ra and other Ra-isotopes and a second extraction chromatography for separating .sup.225Ac from .sup.210Po and .sup.210Pb. The finally purified .sup.225Ac can be used to prepare compositions useful for pharmaceutical purposes.

Claims

1-50. (canceled)

51. A method for purification of .sup.225Ac from irradiated .sup.226Ra-targets provided on a support, comprising the following steps: a) leaching .sup.225Ac and .sup.226Ra from one or more .sup.226Ra-targets with a nitric acid solvent under refluxing conditions to generate an .sup.225Ac and .sup.226Ra containing extracts in a HNO.sub.3 solution with a concentration between 0.1M and 0.2M; b) concentrating the .sup.225Ac and .sup.226Ra containing extract, wherein the concentrating results in a .sup.225Ac and .sup.226Ra containing extract having a concentration of about 1.5 M to about 10 M of HNO.sub.3; c) separating .sup.225Ac from .sup.226Ra, and other Ra isotopes by means of at least one first extraction chromatography with a solid support material having a first extractant system coated thereon, comprising at least one compound in accordance with general formula I in at least one compound in accordance with general formula II, ##STR00008## wherein in formula I: R1, R2 independently is octyl, n-octyl, phenyl, or phenyl substituted with C.sub.1 to C.sub.3 alkyl; R3, R4 independently is propyl, isopropyl, butyl, or isobutyl; wherein in formula II: R5, R6, and R7 independently is C.sub.2-C.sub.5 alkyl, in particular, butyl, or isobutyl; d) allowing the .sup.226Ra to flow through and then eluting .sup.225Ac retained on the solid support with diluted nitric or hydrochloric acid; e) separating .sup.225Ac from .sup.210Po and .sup.210Pb by means of at least one second extraction chromatography with a solid support material having a second extractant system coated thereon, comprising at least one compound in accordance with general formula III in at least one compound in accordance with general formula IV, ##STR00009## wherein in formula III: R8 and R9 independently is H, C.sub.1-C.sub.6 alkyl, or t-butyl; and wherein in formula IV: R10 is C.sub.4 to C.sub.12 alkyl; f) using 2M HCl as mobile phase; and g) recovering .sup.225Ac as a flow-through separately from .sup.210Po and .sup.210Pb, which are retained on the solid support, wherein the recovery of .sup.225Ac is at least 98% and wherein the combined decontaminating factor of .sup.225Ac to .sup.226Ra is between 10.sup.4 and 10.sup.7.

52. (canceled)

53. (canceled)

54. The method of claim 51, wherein the support is a metal, and is selected from the group consisting of Aluminum or Aluminum alloys, passivated Aluminum, anodized Aluminum, coated Aluminum, Aluminum coated with an element of a Platinum group, precious metals, elements from a Platinum group; and mixtures thereof.

55. (canceled)

56. (canceled)

57. (canceled)

58. The method of claim 51, wherein the first extractant system is octyl(phenyl)-N,N-diisobutylcarbamoylphosphine oxide [CMPO] in tributyl phosphate [TBP].

59. The method of claim 51, wherein the second extractant system is a crown ether in accordance with formula V: ##STR00010## in 1-octanol.

60. The method of claim 51, wherein the second extractant system is 4,4-bis(t-butylcyclohexano)-18-crown-6 in 1-octanol.

61. The method of claim 51, wherein the second extractant system is 4,5-bis(t-butylcyclohexano)-18-crown-6 in 1-octanol.

62. The method of claim 51, wherein the first extraction chromatography of step c) is repeated one or more times.

63. The method of claim 51, wherein the second extraction chromatography of step e) is repeated one or more times.

64. The method of claim 51, further comprising removing Rn from the support or the .sup.225Ac and .sup.226Ra containing extract during step a).

65. The method of claim 64, wherein the Rn is removed by means of a first alkaline trap to neutralize acidic vapours, a subsequent silica trap to absorb water, and a final activated coal trap.

66. The method of claim 51, further comprising a step of recovering a .sup.226Ra flowthrough of step d).

67. The method of claim 51, further comprising a step of eluting .sup.210Po from the solid support of the second extraction chromatography in step g) by means of concentrated nitric acid or concentrated hydrochloric acid.

68. The method of claim 51, wherein a fraction of a purification step is examined by means of - and/or -spectroscopy.

69. The method of claim 51, wherein a fraction of a purification step containing any one of: a).sup.225Ac; b) Ra-isotopes; c) .sup.210Po; and d) .sup.210Pb is subjected to an evaporation step.

70. The method of claim 51, further comprising a step of removing one or more organic impurities from a fraction of a purification step.

71. A pharmaceutically acceptable .sup.225Ac-containing radionuclide composition obtained by the method of claim 51.

72. The method of claim 51, wherein the nitric acid solvent of step a) has a concentration of about 0.1M.

73. (canceled)

74. The method of claim 51, wherein the nitric acid solvent or the hydrochloric acid solvent of step a) is used at a temperature of about 30 to 90 C.

75. The method of claim 65, wherein the activated coal trap is cooled.

76. The method of claim 51, further comprising a step of eluting .sup.210Pb from the solid support of the second extraction chromatography in step g) by means of concentrated hydrochloric acid or EDTA.

77. The method of claim 69, wherein the fraction is evaporated to a wet or a dry residue.

78. The method of claim 69, wherein the fraction is redissolved.

79. The method of claim 70, wherein the step of removing one or more organic impurities from a fraction of a purification step is performed by passing the fraction through a resin comprising a non-ionic acrylic ester polymer.

Description

[0127] Further advantages and features can be seen from the description of examples and the drawings.

[0128] FIG. 1. shows a general scheme for the extraction of .sup.225Ac from .sup.226Ra/AI irradiated targets;

[0129] FIG. 2a. shows a -spectrum of the .sup.226Ra-fraction after first Ra/Ac separation with the RE Resin;

[0130] FIG. 2b. shows a -spectrum of the purified .sup.225Ac-fraction;

[0131] FIG. 3a. shows a -spectrum of .sup.225Ac prior to Po and Pb purification; and

[0132] FIG. 3b. shows a -spectrum of .sup.225Ac after Po and Pb purification.

1. Preparation of Purified .SUP.226.Ra Material for Target Preparation

[0133] A Ra batch sealed .sup.226Ra source is pre-checked by -spectrometry, ampoule is broken. The Ra salts or compounds are dissolved and the solution is separated from glass by filtration. The filter and glass particles are leached out with 0.5 M HNO.sub.3 and pooled with .sup.226Ra-containing liquid. This solution is subjected to an at least one extraction chromatography step, which results in a purified Ra fraction.

[0134] The latter fraction is usedafter a further concentration stepfor preparing the .sup.226Ra targets.

[0135] Further details of .sup.226Ra purification for cyclotron target preparation for .sup.226Ac manufacture are described in the not prepublished DE 102005043012, filed on 9 Sep. 2005. The disclosure of this patent application is herewith incorporated by reference in its entirety.

2. Preparation of a .SUP.226.Ra Target by Electrodeposition by Means of a Fixed Aluminium Disc as Cathode

[0136] The present invention will be illustrated by way of an example of a target preparation by means of an electrodeposition according to DE 103 47 459 B3, Radium-Target sowie Verfahren zu seiner Herstellung.

[0137] The person having average skill in the art will understand that the invention also works in targets prepared by the evaporation method in accordance with DE 10 2004 022 200 A1 Method for producing .sup.226Ra targets by the droplet-evaporation methods for irradiation in the cyclotron.

[0138] For the preparation of a .sup.226Ra target, aluminium discs with a thickness of 0.015 mm and a diameter of about 5 cm with a minimal 99% purity of the aluminium are punched out and fixed on a stainless steel support. The support facilitates the handling of the aluminium foils and is removed after the electrodeposition itself, before the positioning of the radium-coated foil in the target itself.

[0139] For the electrodeposition on the aluminium foil, a solution of a radium-226-nitrate is used, whereby in particular 226-radium chloride or 226-radium carbonate are absorbed beforehand for the transformation into the corresponding nitrate in about 0.05 M HNO.sub.3.

[0140] Subsequently, the stainless steel support, on which the aluminium foil is fixed, is weighted and the net weight of the aluminium foil is determined.

[0141] 150 ml (for electrodeposition on aluminium foils with a diameter of up to 15 cm) or 10 to 11 ml isopropanol are added into an electrodeposition cell (for aluminium foil discs with a diameter up to 2 cm).

[0142] Then the required amount of radium-226 solution is filled into the electrolytic cell and 1-2 ml 0.05 M HNO.sub.3 are added. The total volume of the radium solution and 0.05 M HNO.sub.3 should not exceed about 2 ml, if aluminium foil discs with a diameter of up to 2 cm are used, and 20 ml at the most, if aluminium foil discs with a diameter of up to 15 cm are used. When high radium concentrations are used, a white precipitates may be formed. If this happens, 0.05 MHNO.sub.3 is further added until the precipitation has dissolved. The pH value of the depositing plating solution should preferably be between 4 and 5.

[0143] For the electrodeposition of .sup.226Ra containing material out of the plating solution the electric current is adjusted to about 60 mA and a voltage of about 200V is applied, monitored for a few minutes and, if necessary, readjusted.

[0144] After the electrodeposition of the .sup.226Ra solution has been completed, the plating solution is poured out, the support is rinsed with 2 to 3 ml isopropanol and the cell is disassembled and the aluminium foil is additionally rinsed with about 1 to 2 ml isopropanol.

[0145] Afterwards, the support with the .sup.226Ra coated aluminium foil arranged on it is dried under an infrared lamp until the weight remains constant, in order to render the radium-containing coating anhydrous.

[0146] Afterwards, the stainless steel support with the fixed, coated aluminium foil is weighted and the net mass of the coated aluminium foil is determined. Then the yield is determined from the weighted mass of the .sup.226Ra containing layer.

[0147] An alternative way to monitor the yield of the electrodepositioninstead of weighingis to measure the -activity of .sup.226Ra by means of a high resolution -spectrometer.

[0148] Subsequently, the stainless steel support and the aluminium foil are separated from each other.

[0149] The dry aluminium foil coated with radium compounds is carefully covered with a new aluminium foil and the edges of the aluminium foil with which the Aluminium foil carrying the active layer is fixed are cut off, in order to minimize the amount of aluminium in the target itself.

[0150] For the use as radium target in the proton beam of a cyclotron, a pile of the of the circular disc shaped aluminium foils prepared according to present examples, which are coated with radium-containing material in a ring shaped manner, are piled in a so called target cup.

[0151] For the production of a folded radium target, one or more aluminium foils, in the case of this example, coated on one whole surface with .sup.226Ra are covered in a way with another aluminium foil that the radium containing film is covered entirely. Then, the aluminium foil is folded several times until stripes of about 2 mm are obtained. The folded aluminium foil, which contains the layers of radium-containing material, in particular radium oxides, is then placed into the target for proton irradiation in the cyclotron or in the linear accelerator.

[0152] With the above methods according to DE 103 47 459 B3 and DE 10 2004 022 200 A1, it is possible to obtain highly potent .sup.226Ra targets on aluminium foil of a different thickness with different .sup.226Ra-amounts.

[0153] This method assures in particular to deposit films that are highly homogenous on the aluminium-.sup.226Ra target. This is particularly important for the irradiation of the target in the cyclotron, as the atomic nuclei of radium are thereby exposed homogenously to the proton flux.

[0154] The use of aluminium as substrate for .sup.226Ra offers various advantages for the irradiation in a cyclotron and the subsequent radiochemical processing of the irradiated target. The advantages of the aluminium lie in the nuclear physical and chemical properties of the aluminium:

[0155] Nuclear properties: Aluminium has just one single stable isotope. The activation products formed from the aluminium are very short-lived. The formation of only short lived radionuclides on aluminium facilitates the radiochemical purification of Ac-225 and reduces the cooling time of the target after irradiation. As the loss of energy of protons in aluminium is very low, it is possible to use several thin films of aluminium without substantial reduction of the proton energy.

[0156] Physical properties: Aluminium is a light metal with good thermal and electrical conductivity. It is easy to handle and can be adapted easily to the required geometry.

[0157] Chemical properties: Aluminum can easily be dissolved in mineral acids and it can be easily separated from the resulting Actinium. Aluminum foils are available with a high degree of chemical purity and at reasonable prices.

[0158] The deposition of .sup.226Ra, e.g. as oxide or peroxide, allows to obtain a layer with a high content of radium, in particular about 70% of the deposited material per cm.sup.2. The electrodeposition yield is high.

[0159] In practice it has turned out that about 4 to 5 g/cm.sup.2 226Ra with good adhesive properties can be deposited on the aluminum foil.

3. Purification of .sup.225Ac Produced by .sup.226Ra Cyclotron Irradiation with Protons
A. Selective Leaching of Ac and Ra from Irradiated Ra/Al Targets Prepared by the Electrodeposition Technique

[0160] After the irradiation at the cyclotron, the target containing Ac and Ra is transferred to a shielded glove box and positioned in the disassembling and dissolution position. For leaching Ra and Ac from the irradiated Al discs or rings, a refluxing/distillation arrangement is used. This set up enables the condensation of hot water and acids vapours and their continuous reflux into the dissolution vessel and the collection of condensates when this is required. Using this arrangement any Rn which could be still present in the irradiated Al discs can be trapped in a series of traps. The traps are assembled in the following sequence: a NaOH bath to neutralize acid vapors, a silicagel trap to absorb water vapours and finally an activated cooled-coal trap to capture Rn.

[0161] The arrangement used for leaching Ra and Ac from irradiated disc targets is a Refluxing/Destillation arrangement. Typically, the discs or rings are inserted in the flask and they are treated first with 30 ml hot 0.1-0.2 M HNO.sub.3 and then with 30 ml boiling 2M HNO.sub.3 or HCl. The leaching processes are repeated two-three times to wash out any remaining activities of Ra or Ac attached to the discs or to the walls of the glass vessel. The leaching solutions are first subjected to gamma-spectrometry and then combined if required.

[0162] As a result of the leaching process at least two fractions are obtained: the first one contained the Ac, the Ra and part of the activation products (0.1-0.2 M HNO.sub.3) and the second contained most of the matrix (Al) and part of the activation products (2M HNO.sub.3 or concentrated HCl). The 0.1-0.2 M HNO.sub.3 fraction is taken for the Ac extraction process. This solution is converted to 2M HNO.sub.3, during this conversion any particles which can be suspended in solution should be dissolved. The volume of this fraction is generally set to 30 ml.

[0163] The results indicate that more than 99% of Ac and Ra is contained in this fraction. Only trace amounts of Ac and Ra are found in the second leaching solution of 2M HNO.sub.3 which contains most of the Al from the Al discs. The activation products are found almost equally distributed between these two leaching fractions. This procedure facilitates the purification and recycling of Ra because both Ac and Ra are extracted from the foil or mesh without the total dissolution of the Al. In addition, the lower beta and gamma activity associated with activation products in the Ac/Ra leaching solution reduces the risk of radiation damage of the used resins, in particular RE resin.

B. Selective Leaching of Ac and Ra from Irradiated Ra Targets Prepared by the Droplet-Evaporation Technique

[0164] The Ra and Ac are removed from the irradiated Al cup by washing it with a 0.1M HNO.sub.3 solution in an ultrasonic bath. After irradiation at the cyclotron and target disassembling in a shielded glove box; the Al target-cup which carries high radiation dose is transferred and placed into a 250 ml glass beaker (chosen for this specific target cup). This beaker is inserted in an ultrasonic bath. Once the target is inside the beaker or container, 100 mL 0.1M HNO.sub.3 are added into the Al-cup. This volume of 100 ml was selected to completely immerse the target into the leaching solution (the volume depends on the geometry and size of the target cup). The ultrasonic bath is then activated and the temperature of the water bath is kept at approximately 80 C during the process. The leaching process with the ultrasonic bath is conducted two times for short time (not more than 20-30 minutes). All liquid fractions containing the Ra and Ac are combined in a glass beaker and evaporated to wet residues. Experiments with Ba nitrate has previously indicated that Ba at these conditions (setup, leaching volume, duration of US bath) is completely removed. The experiments with Ba also demonstrate that some particulate material associated with Al oxide is released from the target cup. Consequently before starting the separation process, this particulate fraction has to be dissolved either in hot 2M HNO.sub.3 or, if necessary, in 6M HCl and then converted to 2M HNO.sub.3. This solution is taken for the radiochemical separation. The recovery of Ra and Ac from the irradiated target by using this technique is always higher that 90%.

[0165] Studies are being currently carried out to minimize the volume of 0.1M HNO.sub.3 solution needed to quantitatively recover the Ra and Ac from the target cup with a high chemical purity. These studies are conducted using also a new target design. Using this target we will be able to leach out the Ac and Ra from the target cup without the need of disassembling it. The chemical purity of the leaching solution will define the complexity of the Ra recycling and purification process and therefore, it is important to obtain a chemical pure Ra solution already at this stage.

C. Separation of Ac from Ra and Most of the Activation Products by Extraction Chromatography Using the Re Resin as a First Extractant System

[0166] The Ac/Ra separation is based on the use of the extraction chromatography resin RE Resin (EiChrom). In the RE resin, the stationary phase consist of octyl(phenyl)-N,N-diisobutylcarbamoylphosphine oxide in tributylphosphate. This extractant has the property to extract trivalent actinides and lanthanides from nitric acid solutions (e.g. 2M HNO.sub.3). The Ac can be eluted from the stationary phase by washing the column with diluted solutions of nitric or hydrochloric acid (e.g. 0.05M HNO.sub.3).

Background Information

[0167] The extraction of trivalent actinides especially transplutonium elements with bidentate organophosphorus compounds was extensively studied in the USA and the former USSR. In the USA, for example Horwitz et al. (1984, 1993) studied the extraction of Am and other elements with a great number of carbamoylphosphonates and carbamoylphosphine oxides. It was established that both kinds of extractants form trisolvates with lanthanides and trivalent actinides. The high extraction coefficient from nitric acid medium was explained by the bidentate coordination and cycle chromatography versions of the extraction system CMPO/TBP (e.g. TRU resin or RE resin, distributed by EICHROM). On both resins the tetravalent actinides show high retention from nitric acid solutions, having for example capacity factors (CF) in the range of 10.sup.4-10.sup.6 from 2-3 M HNO.sub.3 for the TRU Resin. In the same range of concentration, the CFs for lanthanides is in the order of 100 on the TRU Resin and between 100-200 on the RE Resin. For the RE, the CFs are higher for all relevant elements. The low retention of trivalent actinides from HCl and from diluted nitric acid solutions is the basis for their selective elution. According to Horwitz (1993); Ca, Fe (II) and commonly occurring polyatomic anions do not show significant effect on the Am retention from HNO.sub.3. Based on these properties, the TRU Resin has been applied for the separation of Am from Sr, Ca and Ba in environmental samples (e.g. Burnett et al., 1995; Moreno et al., 1997 and 1998). Burnett et al. (1995) applied the RE Resin in the combined determination of very small quantities of both .sup.226Ra and .sup.228Ra in environmental samples.

[0168] In an entirely novel approach, in the present invention, the inventors have used the RE Resin for the separation of Ac from .sup.226Ra, Al and from most of the activation products produced at the cyclotron by selectively extracting the Ac from 2 M HNO.sub.3. Ac is eluted from the stationary phase using 0.03-0.05 M HNO.sub.3.

[0169] Separation of Ac from Ra, Al and Activation Products after the Irradiation of Ra/AI Targets at the Cyclotron

[0170] FIG. 1 shows the flow chart of processes used for the extraction of Ac from irradiated targets. The size of the columns used (8 mlbed volume) is chosen to maximize the retention of Ac on the RE resin from a large volume of loading solution and consequently to reduce the breakthrough of Ac in the Ra fraction. Assuming that a maximum of 0.5 g Ra and 0.5 g (extreme conditions) of Al can be present in the leaching/loading 2 M HNO.sub.3 solution, a total volume of up to 70-80 ml is needed for the total dissolution of Ra and Al. The results from experiments conducted with synthetic solutions and also with irradiated targets (mg of Ra and hundreds Ci of .sup.225Ac)) indicate that under similar conditions, most of the Ra can be removed by washing the column with approximately 50 ml 2 M HNO.sub.3 without a significant breakthrough of Ac. Meanwhile, most of the Ac can be eluted with 50 ml 0.05 M HNO.sub.3. The typical decontamination factor D.sub.f (Ac/Ra) is found to be in the order of 10.sup.4 (one stage).

D. Purification of the Ac

[0171] D1. From Tracer Quantities of Ra by Using a Repeated Extraction Chromatography Column with the RE Resin

[0172] After the separation of the bulk of Ra, Al and activation products; .sup.210Po (FIG. 3a) and some small quantities of Ra and isotopes of transition elements still remain in the Ac fraction. Therefore, a second separation of Ac from these remaining impurities is necessary. As shown in FIG. 1, the purification process consists of two stages: the first is a repetition of the Ac/Ra separation using the RE resin to provide an additional decontamination of Ac from Ra. The experiments have shown that the total decontamination factor Ac/Ra is approximately 10.sup.6-10.sup.7 by repeating twice the Ac/Ra separation with the RE resin under the described conditions.

[0173] A further purification step enables the Ac/Po, Ac/Pb and Ac/Rn separation using a second extractant system, the Sr Resin (Eichrom) and this process is described below in section D2.

D2. From Po and Pb Isotopes by Using the Sr Resin as a Second Extractant System

Background Information

[0174] In the Sr Resin of the present example, the extractant in the stationary phase is a crown ether: 4,4(5)-bis(t-butylcyclohexaneno)-18-crown-6 in 1-octanol. Horwitz (1991, 1992) proposed this crown ether in 1-octanol to selectively extract Sr from concentrated nitric acid solutions. The extraction chromatography system is commercially available as Sr Resin (Eichrom) and has been applied to the determination of very low activities of .sup.210Pb in environmental samples (Vajda et al.; 1995). Indeed, this resin has been also frequently used for the separation and purification of .sup.90Sr from Ca, Mg and Ba in the radiochemical analysis of environmental samples (Vajda N. et al., 1992; Moreno et al. 1997 and 1998). In the present invention, the inventors have used the Sr Resin as second extractant system to purify Ac from Po, Pb and also Rn in 2 M HCl solutions: while Pb and Po are retained by the stationary phase from 2 M HCl, Ac passes through.

[0175] Separation of Ac from Po and Pb in the Purification Scheme

[0176] The presence of Po in the Ac (FIG. 3a) is observed on the alpha spectrum obtained from the Ac after the RE Resin separation. The presence of both Pb and Po in the Ac can be confirmed by measuring the gross alpha beta activity of aliquots taken from the Ac fraction. Without performing the purification with the Sr Resin, this parameter (gross alpha and beta activities) is much higher that the expected gross activity associated with the Ac and its decay products. Experiments carried out in dynamic conditions demonstrate that while Ac passed through the column, both Po and Pb were retained from 2M HCl acid. The 2M HCl fraction (loading and washing 2M HCl solutions) contained the Ac (FIG. 3b) while Po and Pb were retained by the stationary phase.

E. Final Purification and Pre-Concentration of the Purified Ac Fraction

[0177] Before proceeding with the final preconcentration step, the Ac fraction in 2M HCl acid from the Sr Resin is subject to quality control. At this stage, the radioisotopic purity is generally very high and it depends mainly on the presence of the short living .sup.135La. Consequently the purity quickly increases within a few days after the end of production to more than 99.7%. The activity ratio .sup.226Ra/.sup.225Ac (and also the activity ratio in relation to other long-lived isotopes) is checked and this ratio was usually below 5.10.sup.4 in the Ac fraction.

[0178] If the conditions for radioisotopic purity were not fulfilled, then a further purification of Ac from Ra and other relevant components is required. For this purpose, the Ac fraction obtained after concentration of the 2 M HCl solution is subject to a fast purification from Ra using a 2 mlbed volume column with the RE resin. Usually, there is also a need to purify the Ac from soluble or dispersed organic materials. To separate the organic material, the solution is passed through a pre-filter 2 mlbed volume resin (Eichrom) which contains a non-ionic acrylic ester polymer. The results indicate that the content of soluble organics is decreased in one order of magnitude and all the Ac can be filtered through this resin without retention.

[0179] The results from the manual reprocessing of irradiated Ra/AI targets show that the recovery of Ac and Ra (excluding the recycling and further purification) are higher than 98% and 96% respectively. For processes conducted with 2- to 3 mg of Ra and hundreds Ci of .sup.225Ac and using almost fully automated processes, the recovery factor of Ra is slightly lower but generally higher than 90-92%. This factor is intended to be increased by optimizing parameters associated with the automatic processes (e.g. liquid transfer, dead volumes, etc).

F. Radioisotopic Impurities Measured by -Spectrometry

[0180] The radioisotopic purity and the chemical purity of the Ac depend on the applied radiochemically procedures and also on the purity of the materials (mesh carrier, TC, etc) and reagents (Ra solution, acids, etc). Particularly important is to minimize the content of Sr and Ba which lead to the production of radioisotopes of Y and La respectively that behave similarly to Ac during the separation process.

[0181] As already mentioned in the introduction, several radioisotopes are produced as a result of nuclear reactions type (p,n) or (p,2n) on main impurities like Ba, Fe, Zn, Sr, Pt, V, Ti, Cr and Cu which are present in the Al carrier (foil, mesh) and/or in the Ra deposit. As an example, the -spectrum of a Ra fraction is shown in FIG. 2a. The radionuclides of major contribution to the total gamma activity excluding .sup.226Ra and daughters were typically the following: .sup.135La, .sup.55Co, .sup.56Co, .sup.67Ga, .sup.57Ni, .sup.135mBa, .sup.133mBa, .sup.131Ba, .sup.129Cs, .sup.51Cr, .sup.48V, .sup.52Mn, .sup.54Mn, .sup.65Zn. Except for RE isotopes, most of these radionuclides are separated from the Ac. The typical radioisotopic purity of the purified Ac fraction is higher than 99.8% (see Table 1). The -spectrometry measurements of the purified Ac fraction (FIG. 3b) showed the presence of small quantities of rare earth radioisotopes, namely .sup.87Y, .sup.88Y, .sup.139Ce. Small quantities of .sup.194Au were some times observed (Pt anode) when the target was prepared by electrodeposition (Pt anode).

Radioisotopic Impurities Measured by -Spectrometry

[0182] The -spectrometry results after radiochemical separation of Ra in the aliquot sample indicate that the combined decontamination factor of .sup.225Ac in relation to .sup.226Ra (D.sub.f) is 10.sup.6-10.sup.7. This factor can be significantly improved by optimizing relevant parameters associated with the purification process.

[0183] FIG. 3b shows the spectrum of the purified Ac extracted from an irradiated target. The spectrum clearly shows the peaks of .sup.225Ac and decay products. No impurities of .sup.210Po were observed which indicate that decontamination of .sup.225Ac from .sup.210Po is also very high by applying the described radiochemical scheme (see FIG. 3a).

[0184] The content of impurities will decrease by increasing a proper selection of high purity reagents and materials (e.g. Al foils/mesh of better purity). In addition, when Bi is eluted from the Ac/Bi generator, the rare earth radioisotopes Ce, Ln, Y, and any .sup.226Ra will remain on the stationary phase along with Ac (Ac/Bi generator) thus providing additional purification of .sup.213Bi.

TABLE-US-00002 TABLE 1 Radioisotopic impurities measured in a purified Ac fraction from irradiated target (electrodeposition). Example Activity Activity Radioisotopic Activity ratio ratio purity Radionuclide [Bq] a.sub.I/a.sub.Ac .sup.b a.sub.I, t/a.sub.Ac .sup.c [%] .sup.88Y 4.66 1.57 10.sup.4 4.1 10.sup.4 99.96 .sup.139Ce 7.82 2.64 10.sup.4 .sup.226Ra 0.4.sup.a 1.3 10.sup.5 .sup.209Tl 562 .sup.221Fr 2.93 10.sup.4 .sup.213Bi 2.91 10.sup.4 .sup.225Ac 2.96 10.sup.4 Except for .sup.226Ra, all results were obtained by high resolution gamma-spectrometry .sup.a-spectrometry after radiochemical separation of Ra (two independent analyses) .sup.b a.sub.I/a.sub.Ac impurity/actinium activity ratio .sup.c a.sub.I, t/a.sub.Ac ratio of the activity of all impurities to the activity of .sup.225Ac .sup.55Co, .sup.56Co, .sup.57Co, .sup.58Co, .sup.67Ga, .sup.194Au, .sup.206Bi, .sup.205Bi, .sup.51Cr, .sup.87Y, .sup.48V, .sup.54Mn, .sup.65Zn, .sup.226Ra, .sup.214Pb and .sup.214Bi were not detectable by -spectrometry.

Chemical Impurities Measured in the Purified Ac Fraction

[0185] The typical content of total inorganic impurities in the Ac purified fraction is generally below 100 g. The following elements have been detected and quantified in the Ac fraction: Al, Ba, Ca, Cr, Cu, K, La, Mg, Mn, Na, P, Rb, Si, Sr, Ti, Zr, Zn and Zr.

[0186] Thus, with the method according to the invention a pharmaceutically acceptable .sup.225Ac preparation can be obtained, and the .sup.225Ac can be used for the preparation of nuclear drugs for treatment of cancer as described in the introductory part of the present specification.